\$\begingroup\$The charger is part of the phone. Qi is only a wireless method of providing power to that charger. The charger should behave the same, regardless of where the power comes from.\$\endgroup\$
– JREJul 19 '18 at 14:39

\$\begingroup\$@JRE - As mentioned in my answer, I believe wireless charging is very much a concern to battery life with electronics design, especially with small mobile devices. I know the closers are perceiving this as a usage question, but this has been a big topic in the world of phones and wireless charger design (hence the need for fans).\$\endgroup\$
– BortDec 19 '18 at 16:19

2 Answers
2

The presence or not of (QI) wireless charging by itself bears no relation to how long the battery will last.

The presence of wireless charging does allow you to often charge the battery (for a short time). That then could allow you to keep the battery level between 30% and 70 % for example and that does prolong battery life as less time is spend below 30% and above 70% is most stressful for a battery.

So if you never use Wireless charging or just charge in the same way as you would when charging using a cable, then wireless charging should not affect battery life.

Different battery chemistries react differently. Lead acids are more resilient than the now dominant li-ion batteries. The li-ion cells should be (and will be by any reputable manufacture) monitored for temperature. Charging systems often reduce or halt charging above certain thresholds.

Wireless charging typically causes additional heat due to electrical inefficiencies of both the wireless charging pad and the phone's receiving circuitry. I have personally observed my phones' reported battery temperature to rise in excess of 50°C (122°F). My older phones didn't even bother to warn me, and would eventually just shut down. Flashlight and WIFI are commonly disabled when phones are too hot. The later phones have given me a warning, and my S7 actually goes into some sort of "overheat" mode that disables most background processing in an attempt to mitigate shutting down.

Some wireless chargers have fans in them (especially the "quick charge" varieties that use more than the standard 5V input). One QI charger I have uses a fan to cool the pad's internal circuitry, but does not directly cool the phone at all (bummer).

To reiterate, wireless charging itself does not directly degrade battery life, but a resulting temperature increase can. This will depend on the charger and device being charged. It could be said that if the heat from the wireless charging is kept away from the battery cells, then the battery wouldn't notice the difference between QI and a direct plug in charge. This is not always the case, especially with small devices like phones. If the device stops charging to prevent over-heat, then the battery life is prolonged by an amount that depends on the over-heat threshold.